Suchergebnisse

Context. Nuclear star clusters (NSCs) at the dynamical center of galaxies appear to have a complex star formation history. This suggests repeated star formation, even in the influence of the strong tidal field from supermassive black holes. Although the central region of our Galaxy is an ideal target for studies of the star formation history in the NSCs, most studies in the past have concentrated on a projected distance of R = 0.5-3 pc from the supermassive black hole Sgr A∗. Aims. In our previous study, we detected 31 so far unknown early-type star candidates throughout the Galactic NSC (at R = 0.5-3 pc). They were found via near-infrared (NIR) imaging observations with narrow-band filters which are sensitive to CO absorption lines at ~2.3 μm, a prominent feature for old, late-type stars. The aim of this study is to confirm the spectral type for the early-type star candidates. Methods. We have carried out NIR spectroscopic observations of the early-type star candidates using Subaru/IRCS/AO188 and the laser guide star system. K-band spectra for 20 out of the 31 candidates and reference late-type stars were obtained. By determining an equivalent width, EW(CO), of the CO absorption feature at ≠2.294 μm, we have derived an effective temperature and a bolometric magnitude for each candidate and late-type star, and then constructed an HR diagram. Results. No young (~Myr) massive stars are included in the 20 candidates we observed; however, 13 candidates are most likely intermediate-age giants (50-500 Myr). Two other sources have ages of ~1 Gyr and the remaining five sources are old (>1 Gyr), late-type giants. Conclusions. Although none of the early-type star candidates from our previous narrow-band imaging observations can be confirmed as a young star, we find that the photometric technique can distinguish old, late-type giants from young and intermediate-age populations. From the 20 spectroscopically observed candidates, 65% of them are confirmed as being younger than 500 Myr. The intermediate-age stars could be as yet unknown members of a population formed in a starburst ~100 Myr ago. Finding no young (~a few Myr) stars at R = 0.5-3 pc favors the in situ formation scenario for the presence of the young stars at R< 0.5 pc, although we do not completely exclude the possible existence of unknown young, massive stars in the region from our observations. Furthermore, the different spatial distributions of the young and the intermediate-age stars imply that the Galactic NSC is an aggregate of stars that were born in different places and under a variety of physical conditions.© 2016 ESO. ; This work was supported by KAKENHI, Grant-in-Aid for Research Activity Start-up 23840044, Specially Promoted Research 22000005, COE Research 23103001 and 24103508, Grant-in-Aid for Exploratory Research 15K13463, Grant-in-Aid for challenging Exploratory Research 15K13463, and Young Scientists (A) 25707012, and Institutional Program for Young Researcher Overseas Visits. R.S. acknowledges support by grants AYA2010-17631 and AYA2009-13036 of the Spanish Ministry of Economy and Competition, and by grant P08-TIC-4075 of the Junta de Andalucia. R.S. acknowledges support by the Ramon y Cajal programme of the Spanish-Ministry of Economy and Competition. This material is partly based upon work supported, in part, by the National Science Foundation Grant No. 1066293 and the hospitality of the Aspen Center for Physics. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement No. [614922]. ; Peer Reviewed

We report on a multisite photometric campaign on the high-amplitude delta Scuti star V2367 Cyg in order to determine the pulsation modes. We also used high-dispersion spectroscopy to estimate the stellar parameters and projected rotational velocity. Time series multicolour photometry was obtained during a 98-d interval from five different sites. These data were used together with model atmospheres and non-adiabatic pulsation models to identify the spherical harmonic degree of the three independent frequencies of highest amplitude as well as the first two harmonics of the dominant mode. This was accomplished by matching the observed relative light amplitudes and phases in different wavebands with those computed by the models. In general, our results support the assumed mode identifications in a previous analysis of Kepler data. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. ; South African National Research Foundation; NRF; Bulgarian NSF; South African Astronomical Observatory; UNAM; CONACyT; European Union; Autonomous Region of the Aosta Valley; Italian Department for Work, Health and Pensions; Regional Government of the Aosta Valley; Town Municipality of Nus; Mont Emilius Community; National Research Foundation of South Africa

WOS: 000318232000057 ; We report on a multisite photometric campaign on the high-amplitude delta Scuti star V2367 Cyg in order to determine the pulsation modes. We also used high-dispersion spectroscopy to estimate the stellar parameters and projected rotational velocity. Time series multicolour photometry was obtained during a 98-d interval from five different sites. These data were used together with model atmospheres and non-adiabatic pulsation models to identify the spherical harmonic degree of the three independent frequencies of highest amplitude as well as the first two harmonics of the dominant mode. This was accomplished by matching the observed relative light amplitudes and phases in different wavebands with those computed by the models. In general, our results support the assumed mode identifications in a previous analysis of Kepler data. ; South African National Research FoundationNational Research Foundation - South Africa [73446]; NRF; Bulgarian NSFNational Science Fund of Bulgaria [DO 02-85, DO 02-362, DDVU 02/40-2010]; South African Astronomical ObservatoryNational Research Foundation - South Africa; UNAMUniversidad Nacional Autonoma de Mexico [PAPIIT IN104612]; CONACyTConsejo Nacional de Ciencia y Tecnologia (CONACyT) [CC-118611]; European UnionEuropean Union (EU); Autonomous Region of the Aosta Valley; Italian Department for Work, Health and Pensions; Regional Government of the Aosta Valley; Town Municipality of Nus; Mont Emilius Community; National Research Foundation of South AfricaNational Research Foundation - South Africa ; CU sincerely thanks the South African National Research Foundation for the prize of innovation post doctoral fellowship with the grant number 73446. TG would like to thank NRF Equipment-Related Mobility Grant-2011 for travel to Turkey to carry out the photometric observations. IS and II gratefully acknowledge the partial support from Bulgarian NSF under grant DO 02-85. DD acknowledges for the support of grants DO 02-362 and DDVU 02/40-2010 of Bulgarian NSF. LAB thanks the South African National Research Foundation and the South African Astronomical Observatory for generous financial support. HAK acknowledges Carlos Vargas-Alvarez, Michael J. Lundquist, Garrett Long, Jessie C. Runnoe, Earl S. Wood, Michael J. Alexander for helping with the observations at WIRO. BY wishes to thank EUO for the allocation time of observations during the campaign. LFM acknowledges financial support from the UNAM under grant PAPIIT IN104612 and from CONACyT by way of grant CC-118611. MD, AC and DC are supported by grants provided by the European Union, the Autonomous Region of the Aosta Valley and the Italian Department for Work, Health and Pensions. The OAVdA is supported by the Regional Government of the Aosta Valley, the Town Municipality of Nus and the Mont Emilius Community. TEP acknowledges support from the National Research Foundation of South Africa. This study made use of IRAF Data Reduction and Analysis System and the Vienna Atomic Line Data Base (VALD) services. The authors thank Dr Zima for providing the FAMIAS code.

WOS: 000318232000057 ; We report on a multisite photometric campaign on the high-amplitude delta Scuti star V2367 Cyg in order to determine the pulsation modes. We also used high-dispersion spectroscopy to estimate the stellar parameters and projected rotational velocity. Time series multicolour photometry was obtained during a 98-d interval from five different sites. These data were used together with model atmospheres and non-adiabatic pulsation models to identify the spherical harmonic degree of the three independent frequencies of highest amplitude as well as the first two harmonics of the dominant mode. This was accomplished by matching the observed relative light amplitudes and phases in different wavebands with those computed by the models. In general, our results support the assumed mode identifications in a previous analysis of Kepler data. ; South African National Research FoundationNational Research Foundation - South Africa [73446]; NRF; Bulgarian NSFNational Science Fund of Bulgaria [DO 02-85, DO 02-362, DDVU 02/40-2010]; South African Astronomical ObservatoryNational Research Foundation - South Africa; UNAMUniversidad Nacional Autonoma de Mexico [PAPIIT IN104612]; CONACyTConsejo Nacional de Ciencia y Tecnologia (CONACyT) [CC-118611]; European UnionEuropean Union (EU); Autonomous Region of the Aosta Valley; Italian Department for Work, Health and Pensions; Regional Government of the Aosta Valley; Town Municipality of Nus; Mont Emilius Community; National Research Foundation of South AfricaNational Research Foundation - South Africa ; CU sincerely thanks the South African National Research Foundation for the prize of innovation post doctoral fellowship with the grant number 73446. TG would like to thank NRF Equipment-Related Mobility Grant-2011 for travel to Turkey to carry out the photometric observations. IS and II gratefully acknowledge the partial support from Bulgarian NSF under grant DO 02-85. DD acknowledges for the support of grants DO 02-362 and DDVU 02/40-2010 of Bulgarian NSF. LAB thanks the South African National Research Foundation and the South African Astronomical Observatory for generous financial support. HAK acknowledges Carlos Vargas-Alvarez, Michael J. Lundquist, Garrett Long, Jessie C. Runnoe, Earl S. Wood, Michael J. Alexander for helping with the observations at WIRO. BY wishes to thank EUO for the allocation time of observations during the campaign. LFM acknowledges financial support from the UNAM under grant PAPIIT IN104612 and from CONACyT by way of grant CC-118611. MD, AC and DC are supported by grants provided by the European Union, the Autonomous Region of the Aosta Valley and the Italian Department for Work, Health and Pensions. The OAVdA is supported by the Regional Government of the Aosta Valley, the Town Municipality of Nus and the Mont Emilius Community. TEP acknowledges support from the National Research Foundation of South Africa. This study made use of IRAF Data Reduction and Analysis System and the Vienna Atomic Line Data Base (VALD) services. The authors thank Dr Zima for providing the FAMIAS code.

Up to now, WASP-12b is the only hot Jupiter confirmed to have a decaying orbit. The case of WASP-43b is still under debate. Recent studies preferred or ruled out the orbital decay scenario, but further precise transit timing observations are needed to definitively confirm or refute the period change of WASP-43b. This possibility is given by the Transiting Exoplanet Survey Satellite (TESS) space telescope. In this work, we used the available TESS data, multicolour photometry data obtained with the Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets 2 (MuSCAT2) and literature data to calculate the period change rate of WASP-43b and to improve its precision, and to refine the parameters of the WASP-43 planetary system. Based on the observed-minus-calculated data of 129 mid-Transit times in total, covering a time baseline of about 10 yr, we obtained an improved period change rate of P =-0.6 pm 1.2 ms yr-1 that is consistent with a constant period well within 1σ. We conclude that new TESS and MuSCAT2 observations confirm no detection of WASP-43b orbital decay. © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. ; This work was supported by the Erasmus+ grant number 2017-1-CZ01-KA203-035562, by the VEGA grant of the Slovak Academy of Sciences number 2/0031/18, by an ESA PRODEX grant under contracting with the ELTE University, by the GINOP number 2.3.2-15-2016-00003 of the Hungarian National Research, Development and Innovation Office, and by the City of Szombathely under agreement number 67.177-21/2016. This paper includes data collected with the TESS mission, obtained from the MAST data archive at the Space Telescope Science Institute (STScI). Funding for the TESS mission is provided by the NASA Explorer Program. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5–26555. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This article is based on observations made with the MuSCAT2 instrument, developed by ABC, at Telescopio Carlos Sánchez operated on the island of Tenerife by the IAC in the Spanish Observatorio del Teide. This work was partly financed by the Spanish Ministry of Economics and Competitiveness through grant number PGC2018-098153-B-C31. This work was partly supported by JSPS KAKENHI grant numbers JP17H04574, JP18H01265 and JP18H05439, and JST PRESTO grant number JPMJPR1775. This work was partly supported by Grant-in-Aid for JSPS Fellows, grant number JP20J21872. TP acknowledges support from the Slovak Research and Development Agency – the contract No. APVV-20-0148. MT was supported by MEXT/JSPS KAKENHI grant numbers 18H05442, 15H02063, and 22000005. AC acknowledges financial support from the State Agency for Research of the Spanish MCIU through the 'Center of Excellence Severo Ochoa' award for the Instituto de Astrophysics of Andalusia (SEV-2017-0709). We acknowledge funding from the European Research Council under the European Union's Horizon 2020 research and innovation program under grant agreement number 694513. ; Peer reviewed

Context. We report the discovery of TOI 263.01 (TIC 120916706), a transiting substellar object (R = 0.87 RJup) orbiting a faint M3.5 V dwarf (V = 18.97) on a 0.56 d orbit. Aims. We setout to determine the nature of the Transiting Exoplanet Survey Satellite (TESS) planet candidate TOI 263.01 using ground-based multicolour transit photometry. The host star is faint, which makes radial-velocity confirmation challenging, but the large transit depth makes the candidate suitable for validation through multicolour photometry. Methods. Our analysis combines three transits observed simultaneously in r′, i′, and zs bands usingthe MuSCAT2 multicolour imager, three LCOGT-observed transit light curves in g′, r′, and i′ bands, a TESS light curve from Sector 3, and a low-resolution spectrum for stellar characterisation observed with the ALFOSC spectrograph. We modelled the light curves with PYTRANSIT using a transit model that includes a physics-based light contamination component, allowing us to estimate the contamination from unresolved sources from the multicolour photometry. Using this information we were able to derive the true planet-star radius ratio marginalised over the contamination allowed by the photometry.Combining this with the stellar radius, we were able to make a reliable estimate of the absolute radius of the object. Results. The ground-based photometry strongly excludes contamination from unresolved sources with a significant colour difference to TOI 263. Furthermore, contamination from sources of the same stellar type as the host is constrained to levels where the true radius ratio posterior has a median of 0.217 and a 99 percentile of0.286. The median and maximum radius ratios correspond to absolute planet radii of 0.87 and 1.41 RJup, respectively,which confirms the substellar nature of the planet candidate. The object is either a giant planetor a brown dwarf (BD) located deep inside the so-called "brown dwarf desert". Both possibilities offer a challenge to current planet/BD formation models and make TOI 263.01 an object that merits in-depth follow-up studies. ; With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)